U.S. patent number RE33,718 [Application Number 07/482,265] was granted by the patent office on 1991-10-15 for acoustic transducer with improved electrode spacing.
This patent grant is currently assigned to Knowles Electronics, Inc.. Invention is credited to Elmer V. Carlson, Peter L. Madaffari.
United States Patent |
RE33,718 |
Carlson , et al. |
October 15, 1991 |
Acoustic transducer with improved electrode spacing
Abstract
An acoustic transducer with an improved electret assembly
mounting for providing spacings between the fixed and movable
electrodes, and having as one feature the lowering of the undesired
capacitance therebetween.
Inventors: |
Carlson; Elmer V. (Prospect
Heights, IL), Madaffari; Peter L. (Elgin, IL) |
Assignee: |
Knowles Electronics, Inc.
(Itasca, IL)
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Family
ID: |
27047217 |
Appl.
No.: |
07/482,265 |
Filed: |
February 16, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
907498 |
Sep 15, 1986 |
04730283 |
Mar 8, 1988 |
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Current U.S.
Class: |
367/181; 381/191;
367/170 |
Current CPC
Class: |
H04R
19/01 (20130101); H04R 25/604 (20130101) |
Current International
Class: |
H04R
19/01 (20060101); H04R 19/00 (20060101); H04R
25/00 (20060101); H04R 019/00 () |
Field of
Search: |
;367/140,170,173,174,181,188 ;381/113,116,174,191
;310/324,351,349,350,353,800 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Steinberger; Brian S.
Attorney, Agent or Firm: Wallenstein, Wagner & Hattis,
Ltd.
Claims
We claim: .[.1. An acoustical transducer, comprising in
combination, a case having a top, bottom and side walls; and
electret assembly including a diaphragm having peripheral portions
and a central vibratable plate portion forming a movable electrode,
a diaphragm support ring having an opening thereon mounted in said
case, the peripheral portions of said diaphragm being mountable to
said support ring, a backplate mounted within the opening of said
support ring to form a spacing between the backplate and the
support ring, said backplate having a surface comprising a fixed
electrode and cooperating with the diaphragm movable electrode to
develop a signal, an acoustical chamber formed between the electret
assembly and the bottom of said case, a second chamber formed
between said assembly and the top of said case, said spacing
between the backplate and the support ring lowering the capacitance
between said electrodes, and said spacing
enabling air movement between said chambers..]. .[.2. An acoustical
transducer, comprising in combination, a case having a top, bottom
and side walls; an electret assembly including a diaphragm having
peripheral portions and a central vibratable plate portion having a
conductive material thereon, a diaphragm support ring having an
opening thereon mounted in said case, the peripheral portions of
said diaphragm being mountable to said support ring, a backplate
mounted within the opening of said support ring to form at least
one spacing between the backplate and the support ring, an electret
material, said backplate having a surface on which is electret
material is positioned, said electret material cooperating with the
diaphragm to develop a signal, support posts on the interior
surface of the bottom of the case, protrusions on the surface of
the backplate and aligned with said support posts for supporting
the electret assembly in the case in spaced relation to the bottom
of the case, an acoustical chamber formed between the electret
assembly and the interior surface of the bottom of said case, a
second chamber formed between said assembly and the top of said
case, the spacing between the backplate and electret material and
the support ring lowering the capacitance therebetween and hence
the undesired capacitance affecting the electret assembly, and the
spacing also providing a channel for air between the diaphragm and
the electret material to escape into the second chamber of said
casing..]. .[.3. An acoustical transducer as in claim 2 wherein
said spacing extends substantially around said backplate..]. .[.4.
An acoustical transducer as in claim 2 wherein said diaphragm
includes a flange on its periphery, said flange conforming to the
wall surface of the support ring, and means for adhering said
flange to said ring..]. .[.5. An acoustical transducer as in claim
2 wherein the support ring includes shoulders or projections
extending into said opening, and said backplate is affixed to said
shoulders to provide said at least one spacing between the
backplate and said ring..]. .[.6. An acoustical transducer as in
claim 2 wherein said backplate includes wings or projections
extending outwardly from the edges of said backplate for affixing
said backplate to said
support ring to form said at least one spacing..]. .Iadd.7. An
acoustical transducer comprising, in combination: a case; a
diaphragm having peripheral mounting portions and a central
vibrating plate portion forming a movable electrode, the peripheral
mounting portions of said diaphragm being sealed in said casing to
define separate first and second acoustic chambers on opposite
sides thereof; backplate support means having an opening; a
backplate in said second acoustic chamber confronting said
diaphragm in close but spaced relation thereto, said backplate
being mounted within said opening of said support means and secured
thereto at spaced points and being unsecured thereto and spaced
from the support means and casing between said spaced points of
securement, said spacing between the backplate and support member
and casing between said spaced points of securement extending
substantially around the entire periphery of said backplate so as
to substantially lower the capacitance between said backplate and
the peripheral mounting portions of said diaphragm, the side of
said backplate facing away from said diaphragm being spaced from a
confronting side of said case to define a relatively large space
communicating with the space between said backplate and diaphragm
and constituting the major portion of the volume of said acoustic
chamber on one side of said diaphragm, said backplate having a
layer of electret material thereon and cooperating with said
diaphragm to generate a signal therebetween upon movement of said
diaphragm relative to said backplate or the diaphragm being moved
relative to the backplate when a signal is applied therebetween;
and a pair of electric terminals respectively coupled to said
backplate and diaphragm for coupling a signal to or from the same.
.Iaddend. .Iadd.8. An acoustical transducer as in claim 7 wherein
there are support posts on the interior surface thereof upon which
posts said diaphragm seats and protrusions on the surface of said
backplate contacting said diaphragm outwardly of said central
portion thereof and aligned with said support posts for supporting
said diaphragm in an initial given spaced relation to the
backplate. .Iaddend. .Iadd.9. An acoustical transducer as in claims
7 or 8 wherein said support means is a ring surrounding said
opening therein, said diaphragm includes a flange on its periphery,
said flange conforming to said peripheral surfaces of said support
ring, and including means for adhering said flange to said ring.
.Iaddend. .Iadd.10. An acoustical transducer as in claims 7 or 8
wherein said support means is a ring surrounding said opening
therein, said support ring includes shoulders extending into said
opening, and said backplate is affixed to said shoulders to provide
said spacing between said backplate and said ring. .Iaddend.
.Iadd.11. An acoustical transducer as in claims 7 or 8 wherein said
support means is a ring surrounding said opening therein, said
backplate includes projections extending outwardly from the edges
of said backplate for affixing said backplate to said support ring
and to form said spacing between said support ring and backplate.
.Iaddend. .Iadd.12. An acoustical transducer as in claims 7 or 8
including port means for communicating sound between the outside of
said case and said first acoustic chamber. .Iaddend. .Iadd.13. An
acoustical transducer comprising, in combination: a case; a
diaphragm having peripheral mounting portions and a central
vibrating plate portion forming a movable electrode, the peripheral
mounting portions of said diaphragm being sealed in said casing to
define separate first and second acoustic chambers on opposite
sides thereof; backplate support means having an opening; a
backplate in said second acoustic chamber confronting said
diaphragm in close but spaced relation thereto, said backplate
being mounted within said opening of said support means and secured
thereto at spaced points and being unsecured thereto and spaced
from the support means and casing between said spaced points of
securement, the side of said backplate facing away from said
diaphragm being spaced from a confronting side of said case to
define a relatively large space communicating with the space
between said backplate and diaphragm and constituting the major
portion of the volume of said acoustic chamber on one side of said
diaphragm, said spacing between said backplate and support means
and casing effecting communications between the space between said
diaphragm and backplate and said relatively large space on the
opposite side of said backplate to reduce back pressure on said
diaphragm in said second acoustical chamber; said backplate having
a layer of electret material thereon and said cooperating with said
diaphragm either to generate a signal therebetween upon movement of
said diaphragm relative to said backplate or the diaphragm being
moved relative to the backplate when a signal is applied
therebetween; and a pair of electric terminals respectively coupled
to said backplate and diaphragm for coupling a signal to or from
the backplate and diaphragm. .Iadd.14. The transducer of claim 7
wherein said case has support posts on the interior surface thereof
upon which posts said diaphragm seats, and protrusions on the
surface of the backplate contacting said diaphragm outwardly of the
central portion thereof and aligned with said support posts for
supporting the diaphragm in an initial given spaced relation to the
backplate.
.Iaddend. .Iadd.15. An acoustical transducer as in claims 7 or 8
wherein said support means is a support ring surrounding said
opening therein, said diaphragm includes a flange on its periphery,
said flange conforming to the wall surface of the support ring, and
means for adhering said flange to said ring. .Iaddend. .Iadd.16. An
acoustical transducer as in claims 7 or 8 wherein said support
means is a ring surrounding said opening therein, said support ring
includes shoulders or projections extending into said opening of
said ring, and said backplate is affixed to said shoulders to
provide said spacing between the backplate and said ring. .Iaddend.
.Iadd.17. An acoustical transducer as in claims 7 or 8 wherein said
support means is a ring surrounding said opening therein, said
backplate includes projections extending outwardly from the edges
of said backplate for affixing said backplate to said support ring
and to form said spacing between said support ring and backplate.
.Iaddend. .Iadd.18. An acoustical transducer as in claims 7 or 8
including port means for communicating sound between the outside of
said case and said first acoustic chamber. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention is related to U.S. Pat. No. 4,063,050
entitled "Acoustic Transducer with Improved Electret Assembly"
issued to E. V. Carlson and M. C. Killion and assigned to the same
assignee as the present invention. The disclosure of said patent is
incorporated herein by reference.
The invention relates to an acoustic transducer of the type
comprising an electret assembly including a diaphragm positioned
adjacent a backplate having an electret film formed thereon. The
electret assembly is mounted within a case to form acoustic
chambers on opposite sides of the diaphragm. The case includes a
channel for permitting the external acoustic signal to enter into
one of the acoustic chambers to enable the diaphragm to respond
thereto. Openings are provided to permit the air pulsations created
by the vibrations of the diaphragm to pass from one to the other
acoustic chamber.
The electret comprises a dielectric film deposited on a backplate.
The backplate includes protrusions which rest on support posts
formed in the case to selectively space the dielectric film from
the diaphragm. The electret assembly including the diaphragm and
backplate are conveniently mounted on support posts formed in the
case. The diaphragm extends across the interior of the case and
separates the case into essentially two chambers.
The electret dielectric film is connected to suitable electronic
circuitry to thereby permit electroacoustical interaction of the
diaphragm and electret to provide an electrical signal
representative of the acoustic signal. As is known, the converse
operation may be provided by the transducer in that an electrical
signal may be applied to the electret to cause the diaphragm to
vibrate and thereby develop an acoustic signal which can be coupled
out of the acoustic chamber.
SUMMARY OF THE INVENTION
The present invention is an improvement over the electret assembly
disclosed in above-cited U.S. Pat. No. 4,063,050. In the present
invention, the backplate and the included dielectric film surface
are mounted in the opening of a support ring which in turn is
mounted to the walls of the case. The backplate and dielectric film
which form a charged fixed electrode are positioned within the
support ring to provide a spacing between the edges of the
backplate and the diaphragm. The spacing lowers undesired
capacitance between the backplate electrode and the metalized
diaphragm, which forms a movable electrode. The spacing also
provides a means or way for the air between the diaphragm surface
and the dielectrical material surface to escape into the other
chamber of the case .
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other features, objects and advantages of the
present invention will be apparent from the following more
particular description of the preferred embodiment of the invention
as illustrated in the accompanying drawings wherein:
FIG. 1 is an isometric view, partially in cross section, of an
electret transducer in accordance with the invention;
FIG. 2 is a plan view of case of FIG. 1 with portions thereof
removed to show the mounting of the diaphragm support ring to the
case, and of the backplate to the support ring;
FIG. 3 is an isometric view further illustrating the mounting of
the backplate to the support ring; and
FIG. 4 shows an alternative embodiment of the support ring and the
backplate.
DESCRIPTION OF THE INVENTION
Referring to FIGS. 1, 2 and 3, the electret transducer 11 of the
invention comprises a cup-like case, casing or housing 12 which, in
the embodiment shown, has rectangular shaped walls 15. A mating
cover or top 17 which comprises a generally flat plate fits atop
the walls 15 and is cemented thereon to close the case 12. An
acoustical signal input tube 19 mounted to case 12 communicates to
the interior of case 12 through an acoustical opening, indicated
generally as numberal 40 in end wall 15, and more particularly with
acoustic chamber 20 formed in case 12. An electret transducer
assembly 21 is mounted in case 12. The transducer assembly is
generally of the type described in U.S. Pat. No. 4,063,050, cited
above.
Electret assembly 21 includes a diaphragm 22 having a plate or flat
portion 23 which extends across the relatively flat bottom or lower
surface of case 12 and defines a lower acoustic chamber 20.
Diaphragm 22 may be of polyethylene terephthalate, commonly
available under the trademark MYLAR, or of any similar material.
The plate portion 23 of diaphragm 22 may be coated with a
metallizing layer of conductive material 24, which may be
evaporated on its surface. Diaphragm 22 comprises the movable
electrode of the electret assembly 21.
A backplate 28, which has an dielectric film coating 29 thereon, is
mounted in a support ring 25. Note that the relative thickness of
film coating 29 is exaggerated in the drawings. The backplate 28 is
rectangular in configuration with rounded corners and is mounted in
the rectangular opening 32 of a support ring 25 (see FIGS. 2 and
3). The dimensions of the backplate are slightly smaller than the
opening 32 of the support ring 25 for purposes to be explained.
Backplate 28 comprises the fixed electrode of the electret assembly
21.
The support ring 25 is also rectangular in configuration, and its
outer edges conform to the interior dimensions of the walls 15 of
case 12. The support ring 25 is secured to the interior surface of
the walls 15 such as by a bead of adhesive 43. The support ring 25,
backplate 28 and diaphragm 22 define an upper acoustic chamber 20A
in case 12.
The interior of the rectangular support ring 25 includes inwardly
extending shoulders 30 with a curved inside rim to receive or
conform to the rounded corners of the backplate 28. The backplate
28 thus is positioned within the opening of the support ring 25 and
secured thereto by a nodule of cement 35 placed at the corner
shoulders 30.
Projections or bumps 37 are provided on the lower surface of the
backplate 28, as in the above cited patent, which define the
relative spacing of the backplate to the diaphragm 22. The
projections 37 cooperate with protrusions 16 in the facing portion
of the case 12 to provide a reference for locating the assembly
within the case 12. As described in the cited U.S. Pat. No.
4,063,050, the supporting posts 16 are formed as patterned
indentations or discrete posts mounted in a pattern at the bottom
or interior lower surface 33 of case 12. Posts 16 in the selected
pattern configuration, align with corresponding protrusions 37 on
the backplate 28 and are utilized to support and position the
electret assembly 21 within the case 12. The posts 16 also
accurately define the dimensions of the acoustic chamber 20 which
is formed between the diaphragm 22 and the bottom of case 12.
In assembly, the diaphragm 22 is positioned adjacent to the
backplate 28. As explained above, the spacing between the diaphragm
plate portion 23 and the planar portions of backplate 28 is
controlled by the protrusions 37 on backplate 28. The electret
assembly or subassembly 21 comprising the backplate 28 and
diaphragm 22 can then be inserted into the case 12 to rest on the
posts 16 on the bottom of the case to thus form the acoustic
chamber 20, as noted above.
A non-conductive ceramic plate 41 for containing or supporting the
electronic circuitry is mounted within case 12 by suitable bracing
and or cementing. One edge of plate 41 is mounted in the case 12 by
means of the relatively rigid electrical terminals 47, 48 and 49
each of which have a portion affixed to plate 41 and an opposite
portion which extends as by cementing to terminal pads 54 on the
insulating board 52 mounted to wall 15 of case 12. The ends of the
electrical terminals 47, 49 and 51 which are affixed to plate 41,
also connect to the associated electronic circuitry, as disclosed
in U.S. Pat. No. 4,063,050 which circuitry is mounted on plate 41.
Numeral 51 indicates a grounding tab formed on diaphragm 22 for
electrically connecting with terminal 49; and, reference numeral 52
indicates a weld point from terminal 49 to the case 12. Numeral 45
indicates a connection of backplate 28 to plate 41.
Importantly, and as mentioned above, in the present invention the
spacing 32 is formed between the backplate 28 and support ring 25.
The backplate 28 is smaller than the opening 33 of support ring 25.
Thus other than at the corners, or at other selected supports,
where the backplate 28 is affixed to the support ring 25, such as
by cementing; the spacing 32 is formed around the backplate and the
support ring. In previous constructions, and in contrast to the
present invention, the material of the diaphragm 22, which forms
the movable electrode, closely surrounds the sides of the
backplate. This close spacing forms a capacitor that is in shunt
with the movable portion 23 of the diaphragm 22, which is
responsible for the function of the device. This parasitic
capacitor shares the charge with active portion 23 of the diaphragm
22 thus reducing the signal voltage available as an output to the
associated amplifier. In the present invention, the spacing 32 is
provided between the edge of the backplate 28, fixed electrode and
the diaphragm 22, movable electrode, to lower the undesired
parasitic capacitance. Spacing 32 also provides a means for the air
trapped between the diaphram surface and backplate electret surface
to escape into the larger acoustical chamber 20A of the transducer
case 12.
A second embodiment of the invention is shown in FIG. 4 wherein the
inside corners 36A of the support ring 25A form a 90.degree. angle.
In this embodiment, the backplate 28A is again smaller than the
opening in support ring 25A and includes wings or extensions 37 on
the corners thereof which conform to and abut the corners 36A of
the support ring 25A. The backplate 28A is secured to the support
ring 25A by a nodule of cement 35A placed at each of the corners of
the support ring and the backplate to form the spacing 32.
While the invention has been particularly shown and described with
reference to preferred embodiments thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the spirit and
scope of the invention.
* * * * *